Object positioning in the network: Difference between revisions

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{{Overview|text=Lorem ipsum...}}<br />
{{Overview|text=The RailTopoModel allows for all railway-related physical or logical objects an exact and unique positioning on the network. The generic class EntityLocation serves as a connection holding all positioning information necessary in each case }}<br />
 
== Net Entities and Entity Locations ==
The RailTopoModel data structure is organized around the network. The '''Network''' is used as the main reference system for positioning of arbitrary information objects. This layer allows the user to project objects and entities on the topology, by referencing topology elements.
To define all types of entity, a generic class is defined: '''NetEntity'''. This class defines a general relation with a shared location to define the position on the network. The location of each entity on the network is defined using the intrinsic reference of net element.
NetEntities, specialised as LocatedNetEntities, are located by assigning  '''EntityLocations''' to them. An EntityLocation connects an Entity to the Network via one or more '''PositioningNetElement'''s.


The RailTopoModel data structure is centered around the network. The Network is used as the main reference system for positioning of arbitrary information objects. These information objects are modelled as a generic class called “NetEntity”.<br />
This layer allows the user to project objects and entities on the topology, by referencing topology elements. Three types of generic entities, that can be located on the network, were identified:
# Spot entity: Happens at a point (e.g.: signals, buffer stops, ETCS balise, etc.)
# Linear entity: Happens along a path (e.g.: platform, speed limit, ballast renewal, etc.)
# Areal entity: Happens on a sub network (e.g.: catenary cases, track circuits zones, switches, stations, tunnels, bridges, etc.)
One entity can have more than one location.
<gallery>
<gallery>
File:ObjectTypes.png|Object Types (© InfraBel)
File:ObjectTypes.png|Object Types (© InfraBel)
</gallery>
</gallery>
To define all types of entity, a generic class is defined: '''NetEntity'''. This class defines a general relation with a shared location to define the position on the network. The location of each entity on the network is defined using the intrinsic reference of net element. Thus, three types of entity are defined:


[[File:LocationsLU.png|thumbnail|Locations (Language Unit)]]
[[File:LocationsLU.png|thumbnail|Locations (Language Unit)]]
Each “NetEntity” instance possesses an unspecified number of “EntityLocation” instances. Each “EntityLocation” instance is specialised either as “AreaLocation”, “LinearLocation” or “SpotLocation”.<br />
Each “NetEntity” instance possesses an unspecified number of “EntityLocation” instances. Each EntityLocation instance is specialised as one of three types used to locate different types of NetEntities on the network:
Using an “AreaLocation” instance for connecting to network means that the “NetEntity” in question is related to a subset of “NetElement” instances which together resemble an area or a sub-network.<br />
# SpotLocation: used for information objects happening at a point (e.g.: signals, buffer stops, ETCS balise, etc.)
A connection based on a “LinearLocation” instance means that the “NetEntity” in question is related to a linear segment of the “Network”.<br />
# LinearLocation: used for information objects happening along a path (e.g.: platform, speed limit, ballast renewal, etc.)
A connection based on a “SpotLocation” means that the “NetEntity” in question is related to a “NonLinearElement” building block of the “Network”.<br />
# AreaLocation: used for information objects happening on a sub network (e.g.: catenary cases, track circuits zones, switches, stations, tunnels, bridges, etc.)
<br />
<br />
<br />
A NetEntity can have more than one EntityLocation in the Network, For example:
* An object can be located by some positioning system, and additionally by intrinsic positioning. See later explanations
* A level crossing of two tracks is located on each of those tracks by (at least) one SpotLocation.
* A switch has an AreaLocation (see picture), but can as well be located at its branching point by a SpotLocation
* A station on the micro level of the network is represented by an ArealLocation. On the macro level it is condensed as operational point to a single topological node (NonLinearElement) and therefore is assigned a SpotLocation
The last two examples show that a stringent  classification of  NetEntities into three types, Spot Entity, Linear Entity and Areal Entity is not always possible.
<br />
<br />
<br />
<br />


=== AreaLocation (SubNetwork) ===
== Relating EntityLocations to the Network ==
[[File:AreaLocationLU.png|thumbnail|AreaLocation (Language Unit)]]
 
The three types of EntityLocations are related in different ways to the network. Using an “AreaLocation” instance for connecting to network means that the “NetEntity” in question is related to a subset of “NetElement” instances which together resemble an area or a sub-network. <br/>
A connection based on a “LinearLocation” instance means that the “NetEntity” in question is a path related to a linear segment of the “Network”.<br/>
A connection based on a “SpotLocation” means that the “NetEntity” in question is either related to a “NonLinearElement” building block of the “Network” or it is related to a specified position on a linear NetElement
 
=== SpotLocation ===


A spot entity can be located either at a nonlinear element or along a section of rail/section of line (linear net element) at a certain distance. <br/>
If it is located at a nonlinear element, it could be that happens “in” the element (regardless to orientation). In this case, it encompasses the whole nonlinear element. Otherwise it happens with respect to some relation of the nonlinear element (exit or entry via another net element, for example from an adjacent track edge X). It should then be described as track edge X at 0 (or 100%), meaning it happens at the nonlinear elements centroid, but only on this particular track edge.
<gallery>
<gallery>
File:AreaLocationExample.png|AreaLocation Example (© InfraBel)
File:SpotLocationModified.PNG|SpotLocation Example (© InfraBel, DB Netz)
</gallery>
</gallery>


An areal object is a sub graph (a continuous fraction of the network), that is comprehended as an object.<br />
If it happens along a track edge at a certain distance from the start, it is necessary to define whether this entity happens directly on the track edge, or alongside the track edge; and if the entity occurs in both directions or only in one. These types of entities are located on the network by the type of class: SpotLocation. It is possible to have more than one location for a punctual entity:
It is defined analogously to spot- and linear entities, by listing the ElementParts member of the location.
# Multiple location (on multi-track) on the network for the same level (micro,…).
 
# Multiple location because the entity is located on different levels.
The name areal object was chosen because most practical examples resemble an area. In the context of RailTopoModel an “AreaLocation” instance defines a subgraph (a continuous fraction of the network).<br />
It is produced by listing the ElementParts member of the location.
<gallery>
<gallery>
File:ElementPartsAL.png|Element parts for AreaLocation (© InfraBel)
File:MultipleSpotLocation.png|Example multiple spot location (© InfraBel)
</gallery>
</gallery>


If a nonlinear element is included in a collection, then the whole element is included. If only one track edge is concerned, then the entity should be referenced to the track edge at position 0% (or 100%) to show it happens only on this track edge. It must be checked that the objects included in the areal location form a connected sub graph (no independent parts) and that no object is listed twice.
[[File:SpotLocationLU.png|thumbnail|SpotLocation (Language Unit)]]
In terms of RTM, a SpotLocation is related to exactly one PositioningNetElement, which could be either nonlinear or linear. This means that the NetEntity in question is located on this NetElement and its applicationDirection refers to the NetElement’s orientation. In case the NetElement is linear, the exact place of the SpotLocation remains is specified depending the SpotLocations type:


This type is located by the type of class: '''AreaLocation'''. The area location, in this case, is defined by a set of net elements with a pair of positions (beginning and end in intrinsic reference) for all elements.
===== SpotLocationCoordinate =====
A SpotLocation of this type is related to a PositioningSystemCoordinate which refers to a specific PositioningSystem. This is either a LinearPositioningSystem or a GeometricPositioningSystem.  The PositioningSystemCoordinate provides the exact localization of the SpotLocation


===== SpotLocationIntrinsic =====
A SpotLocationIntrinsic carries the intrinsicCoordinate in reference to the chosen PositioningNetElement, as a value between 0 and 1.
<br/>
In the example spot location on the image above, we see a SpotLocation for a SpotEntity (signal), on netElement A, which is a linear element. The applicationDirection in this case is “reverse”, since the signal is valid in direction 1 to 0 on A.
<br/><br/>The NetEntity "happens" at a certain distance left from A. As a SpotLocationIntrinsic, its intrinsicCoord is 0.5. As a SpotLocationCoordinate, its external coordinate is X.
<br/><br/>
=== LinearLocation ===
=== LinearLocation ===
[[File:LinearLocationLU.png|thumbnail|LinearLocation (Language unit)]]
[[File:LinearLocationLU.png|thumbnail|LinearLocation (Language unit)]]


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File:LinearLocationExample.png|LinearLocation Example (© InfraBel)
File:LinearLocationExample.png|LinearLocation Example (© InfraBel)
</gallery>
</gallery>
 
 
To describe a path location, a start point, an end point and an ordered list of every encompassed element, is needed.
To describe a path or linear location, a start point, an end point and an ordered list of every encompassed element, is needed. <br/><br/>
The start and end points are point locations, thus either a nonlinear element or a point along a linear element (track edge). The path should be a topological path, meaning that at each nonlinear element only one exit direction can be taken. If the start- or end point is a nonlinear element, this element is fully encompassed within the path.<br/><br/>
The correct ordering of the list should be checked against the topology definition of the network. This could be the task of a validator. The orientation of the path on each track edge can be deduced from the order of the crossed nonlinear elements.
Path locations in RTM are located by the type of class: LinearLocation.
 
[[File:OrderedAssociatedNetElement.png|thumbnail|class diagram OrderedAssociatedNetElement]]
<br/><br/>
A LinearLocation is defined by an ordered sequence of '''AssociatedNetElements'''. Each AssociatedNetElement refers to a linear or nonlinear PositionedNetElement. It either encompasses the whole NetElement or a section at the beginning or end of the linear NetElement (or an arbitrary section in case there is only one AssociatedNetElement) <br/><br/>
The beginning and end of the sections of AssociatedNetElements are given in intrinsic coordinates (between 0 and 1) with respect to the related PositioningNetElement. The parameter keepsOrientation defines if the AssociatedNetElement is oriented along the direction of the NetElement or in reverse direction.  <br/><br/>
The AssociatedNetElements have to be oriented all in the same direction, from the start to the end of the sequence. They form a connected path in the network without gaps or branches. <br/><br/>
 
The position of the LinearLocation within the network itself is now complete. Additionally, more positioning systems can be used for the respective entity. If the LinearLocation is a LinearLocationCoordinate, it can be assigned a position with respect to an external – linear or geometric – PositioningSystem.   
<gallery>
<gallery>
File:ExamplePathLocation.png|Example path location (© InfraBel)
File:LinearLocationModified.png|AssociatedNetElements for linear location (© InfraBel, DB Netz)
</gallery>
</gallery>
The example shows the LinearLocation and its AssociateNetElements with respect to the underlying NetElements. The sequence looks as follows:
{| class="wikitable"
|-
! Nr !! AssociatedNetElement !! netElement !! intrinsicCoordBegin !! intrinsicCoordEnd !! keepsOrientation
|-
| 1 || A' || A || 0.7 || 1 || true
|-
| 2 || B' || B || n/a (nonlinear) || n/a || n/a (nonlinear)
|-
| 3 || C' || C || 0 || 1 || true
|-
| 4 || D' || D || n/a  || n/a || n/a
|-
| 5 || E' || E || 0 || 0.8 || true
|}
'''Remark:''' In this example, all the underlying linear NetElements are oriented in the same direction, as can be seen by the positions of their intrinsic coordinates 0 and 1. In case that a linear NetElement, say E, were oriented in the other direction, the AssociatedNetElement E’ would have to be defined by intrinsicCoordBegin = 0.2, intrinsicCoordEnd = 1 and keepsOrientation = false.


The start and end points are point locations, thus either a nonlinear element or a point along a track edge.<br />
=== AreaLocation (SubNetwork) ===
The path should be a topological path, meaning that at each nonlinear element only one exit direction can be taken.<br />
[[File:AreaLocationLU.png|thumbnail|AreaLocation (Language Unit)]]
If the start- or end point is a nonlinear element, this element is fully encompassed within the path.<br />
The correct ordering of the list should be checked against the topology definition of the network. This could be the task of a validator. The orientation of the path on each track edge can be deduced from the order of the crossed nonlinear elements.<br />
This type is located by the type of class: '''LinearLocation'''. The linear location, in this case, is defined by an ordered set of net elements with a position (in intrinsic reference) for the first and last element.


=== SpotLocation ===
[[File:SpotLocationLU.png|thumbnail|SpotLocation (Language Unit)]]
A spot entity can be either a nonlinear element (happens “in” the element) or an entity along a section of rail/section of line at a certain distance. If it happens in the element, it encompasses the whole nonlinear element. It should be described as track edge X at 0 (or 100%), meaning it happens at the elements centroid, but only on this particular track edge.
<gallery>
<gallery>
File:SpotLocationExample.png|SpotLocation Example (© InfraBel)
File:AreaLocationExample.png|AreaLocation Example (© InfraBel)
</gallery>
</gallery>
 
 
If it happens along a track edge at a certain distance, it is necessary to defined whether this entity happens directly on the track edge, or alongside the track edge; and if the entity occurs in both directions or only in one.
An areal object is an object represented by a subgraph (a continuous fraction of the network), that is comprehended as an object. The name areal object was chosen because most practical examples resemble an area. The respective AreaLocation is this subgraph or sub-network. Example: the track network belonging to an organisational unit such as a station. <br/>
These types of entities are located on the network by the type of class: SpotLocation. It is possible to have more than one location for a punctual entity:
It is defined analogously to spot- and linear entities, by listing the AssociatedNetElements of the location, with a pair of positions (beginning and end in intrinsic reference on the respective PositionedNetElement) for all AssociatedNetElements<br/><br/>
# Multiple location (on multi-track) on the network for the same level (micro,…).
The difference to LinearLocation is that the set of AssociatedNetElements does not have to be ordered and can have different orientations. Further there can be branches within the subgraph
# Multiple location because the entity is located on different levels.
 
<br/><br/>
 
As in the case of LinearLocations, if a nonlinear element is included in the collection of AssociatedNetElements, then the whole element is included. The collection can include sections of linear elements, defined by their intrinsic begin and end coordinate. It must be checked that the objects included in the areal location form a connected subgraph (no independent parts) and that no object is listed twice. <br/><br/>
<gallery>
<gallery>
File:MultipleSpotLocation.png|Example multiple spot location (© InfraBel)
File:AreaLocationModified.PNG|AssociatedNetElements for the above AreaLocation (© InfraBel, DB Netz)
</gallery>
</gallery>
The AreaLocation in the example contains 8 AssociatedNetElements. Note that element E is fully included in E’, but not the adjacent  nonlinear NetElement (node) in the network. The track edges A and G are oriented reverse to each other, which does not matter in an AreaLocation.
<br/><br/>
== Assumptions  ==
# ''ElementPart'' is a class needed for splitting and fusioning NetElements for creating a new Network level. It has no specific role for positioning. Here, ''AssociatedNetElement'' is used, as described in the model
# ''SpotLocation'' needs a further attribute ''distance'' to denote the distance of the SpotEntity left or right from the NetElement
# Each linear NetElement has an orientation which means it has a beginning and an end, denoted by intrinsicCoordinates 0 and 1. It has to be defined how this orientation is assigned to the NetElement within the model
# Each AssociatedNetElement refers to one and only one PositionedNetElement. If this is so, then the association netElements of Linearlocation can be eliminated from the model, since it is covered by the netElements relation of AssociatedNetElement (see class diagram above). The model allows one ore more PositionedNetElement, but in case of more than one, where do the intrinsic coordinates or the parameter keepsOrientation refer to?
# The ''applicationDirection'' of a SpotLocation refers to the orientation of the ''netElement'' of the SpotLocation. In the model it is defined with repect to the "LinearLocation" - might be an error.




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|-
|-
| '''What you should have learned'''<br />
| '''What you should have learned'''<br />
Lorem ipsum...
You should be able to
*  
* identify spot-, linear and areal objects in your network and chose the appropriate EntityLocation type (s) for them
* Bulleted list item
* understand the connection of EntityLocations to the network
* ...at last answer the question "where is...?" for every object related to your railway network
|}
|}



Revision as of 17:11, 25 August 2016

Overview
The RailTopoModel allows for all railway-related physical or logical objects an exact and unique positioning on the network. The generic class EntityLocation serves as a connection holding all positioning information necessary in each case


Net Entities and Entity Locations

The RailTopoModel data structure is organized around the network. The Network is used as the main reference system for positioning of arbitrary information objects. This layer allows the user to project objects and entities on the topology, by referencing topology elements. To define all types of entity, a generic class is defined: NetEntity. This class defines a general relation with a shared location to define the position on the network. The location of each entity on the network is defined using the intrinsic reference of net element. NetEntities, specialised as LocatedNetEntities, are located by assigning EntityLocations to them. An EntityLocation connects an Entity to the Network via one or more PositioningNetElements.

Locations (Language Unit)

Each “NetEntity” instance possesses an unspecified number of “EntityLocation” instances. Each EntityLocation instance is specialised as one of three types used to locate different types of NetEntities on the network:

  1. SpotLocation: used for information objects happening at a point (e.g.: signals, buffer stops, ETCS balise, etc.)
  2. LinearLocation: used for information objects happening along a path (e.g.: platform, speed limit, ballast renewal, etc.)
  3. AreaLocation: used for information objects happening on a sub network (e.g.: catenary cases, track circuits zones, switches, stations, tunnels, bridges, etc.)



A NetEntity can have more than one EntityLocation in the Network, For example:

  • An object can be located by some positioning system, and additionally by intrinsic positioning. See later explanations
  • A level crossing of two tracks is located on each of those tracks by (at least) one SpotLocation.
  • A switch has an AreaLocation (see picture), but can as well be located at its branching point by a SpotLocation
  • A station on the micro level of the network is represented by an ArealLocation. On the macro level it is condensed as operational point to a single topological node (NonLinearElement) and therefore is assigned a SpotLocation

The last two examples show that a stringent classification of NetEntities into three types, Spot Entity, Linear Entity and Areal Entity is not always possible.

Relating EntityLocations to the Network

The three types of EntityLocations are related in different ways to the network. Using an “AreaLocation” instance for connecting to network means that the “NetEntity” in question is related to a subset of “NetElement” instances which together resemble an area or a sub-network.
A connection based on a “LinearLocation” instance means that the “NetEntity” in question is a path related to a linear segment of the “Network”.
A connection based on a “SpotLocation” means that the “NetEntity” in question is either related to a “NonLinearElement” building block of the “Network” or it is related to a specified position on a linear NetElement

SpotLocation

A spot entity can be located either at a nonlinear element or along a section of rail/section of line (linear net element) at a certain distance.
If it is located at a nonlinear element, it could be that happens “in” the element (regardless to orientation). In this case, it encompasses the whole nonlinear element. Otherwise it happens with respect to some relation of the nonlinear element (exit or entry via another net element, for example from an adjacent track edge X). It should then be described as track edge X at 0 (or 100%), meaning it happens at the nonlinear elements centroid, but only on this particular track edge.

If it happens along a track edge at a certain distance from the start, it is necessary to define whether this entity happens directly on the track edge, or alongside the track edge; and if the entity occurs in both directions or only in one. These types of entities are located on the network by the type of class: SpotLocation. It is possible to have more than one location for a punctual entity:

  1. Multiple location (on multi-track) on the network for the same level (micro,…).
  2. Multiple location because the entity is located on different levels.
SpotLocation (Language Unit)

In terms of RTM, a SpotLocation is related to exactly one PositioningNetElement, which could be either nonlinear or linear. This means that the NetEntity in question is located on this NetElement and its applicationDirection refers to the NetElement’s orientation. In case the NetElement is linear, the exact place of the SpotLocation remains is specified depending the SpotLocations type:

SpotLocationCoordinate

A SpotLocation of this type is related to a PositioningSystemCoordinate which refers to a specific PositioningSystem. This is either a LinearPositioningSystem or a GeometricPositioningSystem. The PositioningSystemCoordinate provides the exact localization of the SpotLocation

SpotLocationIntrinsic

A SpotLocationIntrinsic carries the intrinsicCoordinate in reference to the chosen PositioningNetElement, as a value between 0 and 1.
In the example spot location on the image above, we see a SpotLocation for a SpotEntity (signal), on netElement A, which is a linear element. The applicationDirection in this case is “reverse”, since the signal is valid in direction 1 to 0 on A.

The NetEntity "happens" at a certain distance left from A. As a SpotLocationIntrinsic, its intrinsicCoord is 0.5. As a SpotLocationCoordinate, its external coordinate is X.

LinearLocation

LinearLocation (Language unit)

Many “NetEntity” instances can be seen as paths.

To describe a path or linear location, a start point, an end point and an ordered list of every encompassed element, is needed.

The start and end points are point locations, thus either a nonlinear element or a point along a linear element (track edge). The path should be a topological path, meaning that at each nonlinear element only one exit direction can be taken. If the start- or end point is a nonlinear element, this element is fully encompassed within the path.

The correct ordering of the list should be checked against the topology definition of the network. This could be the task of a validator. The orientation of the path on each track edge can be deduced from the order of the crossed nonlinear elements. Path locations in RTM are located by the type of class: LinearLocation.

class diagram OrderedAssociatedNetElement



A LinearLocation is defined by an ordered sequence of AssociatedNetElements. Each AssociatedNetElement refers to a linear or nonlinear PositionedNetElement. It either encompasses the whole NetElement or a section at the beginning or end of the linear NetElement (or an arbitrary section in case there is only one AssociatedNetElement)

The beginning and end of the sections of AssociatedNetElements are given in intrinsic coordinates (between 0 and 1) with respect to the related PositioningNetElement. The parameter keepsOrientation defines if the AssociatedNetElement is oriented along the direction of the NetElement or in reverse direction.

The AssociatedNetElements have to be oriented all in the same direction, from the start to the end of the sequence. They form a connected path in the network without gaps or branches.

The position of the LinearLocation within the network itself is now complete. Additionally, more positioning systems can be used for the respective entity. If the LinearLocation is a LinearLocationCoordinate, it can be assigned a position with respect to an external – linear or geometric – PositioningSystem.

The example shows the LinearLocation and its AssociateNetElements with respect to the underlying NetElements. The sequence looks as follows:

Nr AssociatedNetElement netElement intrinsicCoordBegin intrinsicCoordEnd keepsOrientation
1 A' A 0.7 1 true
2 B' B n/a (nonlinear) n/a n/a (nonlinear)
3 C' C 0 1 true
4 D' D n/a n/a n/a
5 E' E 0 0.8 true

Remark: In this example, all the underlying linear NetElements are oriented in the same direction, as can be seen by the positions of their intrinsic coordinates 0 and 1. In case that a linear NetElement, say E, were oriented in the other direction, the AssociatedNetElement E’ would have to be defined by intrinsicCoordBegin = 0.2, intrinsicCoordEnd = 1 and keepsOrientation = false.

AreaLocation (SubNetwork)

AreaLocation (Language Unit)

An areal object is an object represented by a subgraph (a continuous fraction of the network), that is comprehended as an object. The name areal object was chosen because most practical examples resemble an area. The respective AreaLocation is this subgraph or sub-network. Example: the track network belonging to an organisational unit such as a station.
It is defined analogously to spot- and linear entities, by listing the AssociatedNetElements of the location, with a pair of positions (beginning and end in intrinsic reference on the respective PositionedNetElement) for all AssociatedNetElements

The difference to LinearLocation is that the set of AssociatedNetElements does not have to be ordered and can have different orientations. Further there can be branches within the subgraph



As in the case of LinearLocations, if a nonlinear element is included in the collection of AssociatedNetElements, then the whole element is included. The collection can include sections of linear elements, defined by their intrinsic begin and end coordinate. It must be checked that the objects included in the areal location form a connected subgraph (no independent parts) and that no object is listed twice.

The AreaLocation in the example contains 8 AssociatedNetElements. Note that element E is fully included in E’, but not the adjacent nonlinear NetElement (node) in the network. The track edges A and G are oriented reverse to each other, which does not matter in an AreaLocation.



Assumptions

  1. ElementPart is a class needed for splitting and fusioning NetElements for creating a new Network level. It has no specific role for positioning. Here, AssociatedNetElement is used, as described in the model
  2. SpotLocation needs a further attribute distance to denote the distance of the SpotEntity left or right from the NetElement
  3. Each linear NetElement has an orientation which means it has a beginning and an end, denoted by intrinsicCoordinates 0 and 1. It has to be defined how this orientation is assigned to the NetElement within the model
  4. Each AssociatedNetElement refers to one and only one PositionedNetElement. If this is so, then the association netElements of Linearlocation can be eliminated from the model, since it is covered by the netElements relation of AssociatedNetElement (see class diagram above). The model allows one ore more PositionedNetElement, but in case of more than one, where do the intrinsic coordinates or the parameter keepsOrientation refer to?
  5. The applicationDirection of a SpotLocation refers to the orientation of the netElement of the SpotLocation. In the model it is defined with repect to the "LinearLocation" - might be an error.


What you should have learned

You should be able to

  • identify spot-, linear and areal objects in your network and chose the appropriate EntityLocation type (s) for them
  • understand the connection of EntityLocations to the network
  • ...at last answer the question "where is...?" for every object related to your railway network


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